As gas turbine engine designers and manufacturers seek to increase engine performance and efficiency, one known solution is to incorporate a counter-rotating turbine. However, counter-rotating turbines generally excite or increase vibratory modes due to the sum of the inner and outer rotor speed. Additionally, relatively larger diameters and small radial depths of overhanging or cantilevered shrouds of counter-rotating turbine engines may define relatively low natural frequencies or low order vibratory modes, thus limiting engine speeds and/or subjecting the engine to undesired vibratory modes.
Known counter-rotating turbine engines adversely offset efficiency and performance improvements of a counter-rotating arrangement with larger and/or heavier structures to mitigate certain vibratory modes. Thus, there is a need for structures that mitigate certain vibratory modes of counter-rotating turbine engines.